Contiguously Increasing Numbers - Amazon Top Interview Questions

Problem Statement :

Given two integers start and end, return a sorted list of integers such that every number e is between start ≤ e ≤ end and the digits of e are contiguously increasing. For example, 2345 is contiguously increasing while 135 and 321 are not.


0 ≤ start ≤ end < 2 ** 31

Example 1


start = 0
end = 100


[1, 2, 3, 4, 5, 6, 7, 8, 9, 12, 23, 34, 45, 56, 67, 78, 89]

Solution :


                        Solution in C++ :

vector<int> solve(int start, int end) {
    vector<int> ans;
    queue<int> q;
    for (int i = 1; i <= 9; i++) q.push(i);

    while (!q.empty()) {
        int sz = q.size();
        while (sz--) {
            int cur = q.front();
            if (cur >= start and cur <= end) ans.push_back(cur);

            if (cur % 10 != 9) {
                cur = cur * 10 + cur % 10 + 1;

    return ans;

                        Solution in Python : 
class Solution:
    def solve(self, start, end):
        s = "123456789"
        a = []
        for i in range(9):
            for j in range(i + 1, 10):
                x = int(s[i:j])
                if start <= x <= end:
                    a += (x,)
        return sorted(a)

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